Ross xpress lens construction 4 or 5 element?

The Ross ensign Xpress 105mm f 3.8 is usually said to be a 4 element

tessar type lens but someone somewhere on photo.net (I think)

suggested that it is infact a 5 element lens pretending to be a 4

element lens to avoid objection from zeiss concerning the

construction of their 5 element designs.

 

Does anyone have any information on this?

 

Regards

 

Bob

i have an example of the same ross lens bunged into a bess ii body. i just unscrewed the elements, and frankly it looks more like a triplet than anything else. i'm guessing that it is a tessar, but with cemented elements where there should be the airspace. no way it's a planar type (to stick with the Z terminology). whether different designs were used at different times for this underrated optic, i do not know. ivor matanle is a ross fiend. if i can dig up his email address, i will pass it along.

I have since found the comment burried very deep in a contribution by Jerry Friedman on 645 v 6x7 formats but would be interested in any further information that may be available.

 

Bob

Everything I've read on that lens says 4 element. Also,many of them from even the 1950's are uncoated. I almost bought a camera with that lens until I found out the lens was not coated.

andrew, i share your misgivings about uncoated lenses. flare robs sharpness/contrast long before it is recognized as flare. BUT, the ross lens is surprisingly good AND you can use the voigtlander skopar/heliar 105mm f3.5 shades on the ross (or any other 40.5 shade you have around the house. properly shaded, the optic IS very sharp AND the it has a beautiful tonal range.

My 9th edition (1951) of Optics The Technique of Definition by Arthur Cox says:

"Another modification of the triplet construction is the Ross Xpres lens in which the compounding of the back crown is carried a stage further with the aim of obtaining among other things a still better correction of zonal spherical aberration."

The Xpress seems to be a longer, slower version of the Xpres, covering 50 degrees instead of 45.

The diagram shows what would otherwise be a Tessar except that the cemented rear doublet is instead a triplet, hence 5 elements in 3 groups.

Cox apparently considers the Tessar to be derived from the Cooke Triplet, however, Rudolph Kingslake in A History of the Photographic Lens (1989)says:

"It is certain that the Tessar was not a modified Triplet, as the series of steps followedby Rudolph in going from the Anastigmat to the Tessar are well established, but for some of the later designs it is not always clear whether they should be regarded as modified Tessars or modified Triplets."

About the Xpres:

"The Tessar was such an excellent design that other workers would have liked to copy it but were prevented from doing so by patent limitations. The simplest way out was to use a cemented triplet in the rear instead of a doublet. Several designs of this type appeared in 1913, including the Ross Xpres by J. Stuart and J. W. Hasselkus..."

<p>The Ensign Autorange 820 has a APO Xpres 105/3.8 lens<br>

<a href="http://leicaism.net/?p=47">http://leicaism.net/?p=47</a><br>

Fuuny thing is all web info say it has a Epsilon shutter with top speed of 1/250<br>

But I do know a 820 has a top speed of 1/300!</p>

<p>This is an old post but given someone might search it I thought it best to clear up any doubt.<br>

1) The Ross Xpres 105mm f 3.8 with a front focussing helical - the one that is fitted to teh Ensign Selfix 820 and Selfix Special 820 is a 4 element Tessar type lens<br>

2) The Ross Xpres 105mm f3.8 fitted to the Ensign Autorange 820 is a later improved version with 5 elements and is a Heliar type design.<br>

Both are coated and both are capable of very good results but the Autorange version is the best and is very comparable to modern medium format lenses in terms of image quality. I have a 30"x20" print on the wall and every blade of grass is sharply defined.</p>

<p> </p>